Liquid-ejecting head, liquid-ejecting apparatus, and piezoelectric device

ABSTRACT

There is provided a piezoelectric device comprising a first electrode, a piezoelectric layer that is formed above the first electrode, a second electrode that is formed above the piezoelectric layer and a coating layer that is formed above the second electrode consisting of tungsten or titanium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2010-101925 filed Apr. 27, 2010, the contents of whichare hereby incorporated by reference in their entirety.

BACKGROUND

1. Technical Field

The present invention relates to a liquid-ejecting head, aliquid-ejecting apparatus, and a piezoelectric device.

2. Related Art

A liquid-ejecting head is used as a component of a liquid-ejectingapparatus and is applied to, for example, an ink jet printer. In thiscase, the liquid-ejecting head is used to eject a droplet of ink, andthe ejected droplet then flies. Accordingly, the ink jet printer canperform printing as a result of applying the ink onto a medium such aspaper.

In general, in order to eject a liquid from a nozzle, theliquid-ejecting head has an actuator that applies pressure to theliquid. Some types of actuators have a configuration in which apiezoelectric layer made of a piezoelectric material, such ascrystallized piezoelectric ceramic, that exhibits an electromechanicaltransduction function is disposed between two electrodes. Thepiezoelectric layer can be deformed as a result of application ofvoltage through the two electrodes, and such deformation can be utilizedto bring the actuator into operation, for example, in a bendingvibration mode.

In the actuator having such a configuration, a common upper electrodestructure is known, in which a plurality of piezoelectric layers forpiezoelectric devices are formed and in which an electrode (hereinafteralso referred to as an “upper electrode”) that covers the piezoelectriclayers is formed so as to continuously overlie the plurality ofpiezoelectric devices (JP-A-2009-172878).

In the case where a piezoelectric device has a configuration in whichthe piezoelectric layer is disposed between a lower electrode and anupper electrode, the piezoelectric layer may have an active region andan inactive region, the active region being disposed between twoelectrodes, and the inactive region not being disposed between the twoelectrodes. In this case, in the deformation of the piezoelectric layer,strain of the active region is suppressed by the inactive region withthe result that stress concentrates in the vicinity of a boundarybetween the active region and the inactive region.

Meanwhile, for the purpose of, for example, increasing an amount of aliquid ejected from the liquid-ejecting apparatus, the piezoelectriclayer is required to be deformed in an increased amount. In the casewhere an amount of the deformation is increased, larger stressconcentrates in the vicinity of the boundary between the active regionand the inactive region, and cracking may occur, for example, in thepiezoelectric layer.

SUMMARY

An advantage of some aspects of the invention is that it provides aliquid-ejecting head and a liquid-ejecting apparatus, theliquid-ejecting head having a piezoelectric layer in which cracking isless likely to occur and having good reliability. Furthermore, anotheradvantage of some aspects of the invention is that it provides apiezoelectric device having a piezoelectric layer in which cracking isless likely to occur and having good reliability.

Embodiments of the invention are provided in order to overcome at leasta part of the above disadvantages and have the following aspects oradvantages.

According to a first aspect of the invention, there is provided apiezoelectric device including a first electrode, a piezoelectric layerthat is formed so as to cover the first electrode, a second electrodethat is formed on the piezoelectric layer, and a coating layer that isformed on the second electrode by using any one of tungsten andtitanium. The first electrode and the second electrode form arectangular overlap region in which the first electrode overlaps thesecond electrode in a plan view. The first electrode defines a long sideof the overlap region. The second electrode defines a short side of theoverlap region. The overlap region has a pair of first regions and has asecond region, the pair of the first regions being positioned adjacentto a pair of the short sides, and the second region being positionedbetween the pair of the first regions, in a plan view. The coating layeris formed at least in the first regions so as to avoid the second regionof the overlap region in a plan view.

In the liquid-ejection head having this advantageous configuration, thecoating layer is formed in the vicinity of a boundary between the activeregion and inactive region of the piezoelectric layer of thepiezoelectric device. By virtue of such a configuration, straingenerated in the vicinity of the boundary between the active region andinactive region of the piezoelectric layer can be reduced duringactuation of the piezoelectric device. Accordingly, the concentration ofthe stress generated in the vicinity of the boundary between the activeregion and the inactive region can be reduced, and cracking is thereforeless likely to be caused in the piezoelectric layer. Consequently, theliquid-ejecting head having such a configuration exhibits increasedreliability.

In the above advantageous configuration, it is preferable that thepiezoelectric device has a lead electrode that is formed on thepiezoelectric layer so as to be electrically connected to the firstelectrode and that a material used for the lead electrode is capable ofcontaining nickel and chromium.

In the liquid-ejecting head having this advantageous configuration,galvanic corrosion is less likely to be caused in the lead electrode ofthe piezoelectric device during a production process. Namely, differencebetween standard electrode potential of nickel and chromium and standardelectrode potential of tungsten and titanium is small, and galvaniccorrosion is therefore less likely to be caused, for example, inwet-etching a coating layer made of tungsten or titanium.

In any of the above advantageous configurations, it is preferable that amaterial used for the second electrode is capable of primarilycontaining iridium.

In the liquid-ejecting head having this advantageous configuration, thesecond electrode exhibits good electrical conductivity and protects thepiezoelectric layer.

According to a second aspect of the invention, there is provided aliquid-ejecting apparatus including the liquid-ejecting head having anyof the above advantageous configurations.

The liquid-ejecting apparatus having this advantageous configurationincludes the above liquid-ejecting head and therefore exhibits increasedreliability.

According to a third aspect of the invention, there is provided apiezoelectric device having a first electrode, a piezoelectric layerthat is formed so as to cover the first electrode, a second electrodethat is formed on the piezoelectric layer, and a coating layer that isformed on the second electrode by using any one of tungsten andtitanium. The first electrode and the second electrode form arectangular overlap region in which the first electrode overlaps thesecond electrode in a plan view. The first electrode defines a long sideof the overlap region. The second electrode defines a short side of theoverlap region. The overlap region has a pair of first regions and has asecond region, the pair of the first regions being positioned adjacentto a pair of the short sides, and the second region being positionedbetween the pair of the first regions, in a plan view. The coating layeris formed at least in the first region so as to avoid the second regionof the overlap region in a plan view.

In the piezoelectric device having this advantageous configuration, thecoating layer is formed in the vicinity of the boundary between theactive region and inactive region of the piezoelectric layer. By virtueof such a configuration, in the case where an electric field is appliedbetween the first electrode and the second electrode, strain generatedin the vicinity of the boundary between active region and the inactiveregion of the piezoelectric layer can be reduced. Accordingly, theconcentration of the stress generated in the vicinity of the boundarybetween the active region and the inactive region can be decreased, andcracking is therefore less likely to be caused in the piezoelectriclayer. Consequently, the piezoelectric device has high reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a plan view schematically illustrating part of aliquid-ejecting head of an embodiment.

FIG. 2 is a cross-sectional view schematically illustrating part of theliquid-ejecting head of the embodiment.

FIG. 3 is a cross-sectional view schematically illustrating part of theliquid-ejecting head of the embodiment.

FIG. 4 is an exploded perspective view illustrating the liquid-ejectinghead of the embodiment.

FIG. 5 is a perspective view illustrating a liquid-ejecting apparatus ofan embodiment.

FIG. 6 is a graph illustrating results of simulation of relationshipbetween the thickness and strain of a coating layer.

FIG. 7 illustrates an example of a cross-sectional surface of thecoating layer micrographed using a transmission electron microscope.

FIG. 8 illustrates another example of a cross-sectional surface of thecoating layer micrographed using a transmission electron microscope.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Preferred embodiments of the invention will be hereinafter describedwith reference to the drawings. The following embodiments are employedto describe an example of embodiments of the invention. Accordingly,embodiments of the invention are not limited to the followingembodiments and include various modifications without departing from thescope of the invention. Not all the configurations to be described withrespect to the following embodiments are required elements ofembodiments of the invention.

1. Liquid-Ejecting Head

FIG. 1 is a plan view schematically illustrating part of aliquid-ejecting head 1000 of this embodiment. FIG. 2 is across-sectional view schematically illustrating the liquid-ejecting head1000 of this embodiment. FIG. 3 is another cross-sectional viewschematically illustrating the liquid-ejecting head 1000 of thisembodiment. In addition, FIG. 2 illustrates a cross-sectional surfacetaken along the line II-II in FIG. 1, and FIG. 3 illustrates across-sectional surface taken along the line III-III in FIG. 1.

The liquid-ejecting head 1000 of this embodiment at least has apiezoelectric device 100.

1.1 Piezoelectric Device

The piezoelectric device 100 has a substrate 1, a first electrode 10, apiezoelectric layer 20, a second electrode 30, and a coating layer 40.In the case where the substrate 1 has flexibility and functions as avibrating plate (insulating layer) that can be deformed (bent) as aresult of actuation of the piezoelectric layer 20, the piezoelectricdevice 100 serves as a piezoelectric actuator 102 that is vibrated.

1.1.1. Substrate

The substrate 1 has a planar shape. The substrate 1 can exhibitflexibility and may be provided in the form of a vibrating plate(insulating layer) that can be deformed (bent) as a result of actuationof the piezoelectric layer 20. In the case where the substrate 1 servesas a vibrating plate, examples of a material used for the substrate 1include an inorganic oxide and inorganic nitride such as zirconiumdioxide (ZrO₂), silicon nitride, silicon oxide, or aluminum oxide andinclude an alloy such as stainless steel. Among these, zirconium dioxideis an especially preferable material of the substrate 1 (vibratingplate) in terms of chemical stability and rigidity. The substrate 1 mayhave a structure in which two or more of the above materials arestacked.

A silicon substrate or a quartz substrate may be employed as thesubstrate 1. In this case, the substrate 1 is formed, for example, in atuning fork-like shape, and the substrate 1 is oscillated as a result ofactuation of the piezoelectric layer 20. Alternatively, a timing devicecan be configured, in which actuation of the substrate 1 is detected byutilizing the strain of the piezoelectric layer 20. In this case,several types of piezoelectric devices can be configured, such as anultrasonic device, for example an ultrasonic oscillator; a device havinga mechanical output, for example an ultrasonic motor; and a pressuresensor with which the stress applied to the substrate 1 and thedeformation of the substrate 1 are detected by utilizing the strain orthe like of the piezoelectric layer 20.

In this embodiment, the substrate 1 has flexibility and functions as avibrating plate that serves as a wall surface of a pressure chamber ofthe liquid-ejecting head 1000. Accordingly, the actuation of thepiezoelectric layer 20 enables the substrate 1 to be deformed with theresult that the volume of the pressure chamber can be changed, therebybeing able to eject a liquid from a nozzle hole of the liquid-ejectinghead 1000.

1.1.2. First Electrode

The first electrode 10 is formed on the substrate 1. The first electrode10 is covered with the piezoelectric layer 20 and is provided so as tohave an area that forms a structure in which the piezoelectric layer 20is positioned between such an area and the second electrode 30 that isformed on the piezoelectric layer 20. The first electrode 10 is formedon the substrate 1 but is not required to entirely cover the substrate1. The first electrode 10 is provided in the form of a layer, a thinfilm, or a flat plate. For example, the first electrode 10 can beconfigured so as to have a thickness that is in the range from 20 nm to60 nm. In the case where the first electrode 10 has a thickness smallerthan 20 nm, the electrical conductivity of the first electrode 10 mayfall into insufficiency.

Seeing the first electrode 10 in a plan view (in a direction normal tothe substrate 1), the first electrode 10 has a shape with a long side.For example, the first electrode 10 has a rectangular shape in a planarview. In the case where the piezoelectric device 100 has a plurality ofoperable portions, the first electrode 10 can be used for individualelectrodes thereof.

Seeing the first electrode 10 in a plan view, the first electrode 10forms an overlap region 50 in which the first electrode 10 overlaps thesecond electrode 30. The overlap region 50 has a rectangular shape in aplanar view. A long side 50 a of the overlap region 50 is defined by aside, which is parallel to a length direction, of the first electrode10.

In one of the functions of the first electrode 10, the first electrode10 serves as either electrode provided to apply an electric field to thepiezoelectric layer 20 (for example a lower electrode that is formed soas to underlie the piezoelectric layer 20).

Examples of a material used for the first electrode 10 include varioustypes of metals such as nickel, iridium, and platinum; the conductiveoxide thereof (for example, iridium oxide); a composite oxide ofstrontium and ruthenium (SrRuOx: SRO); and a composite oxide oflanthanum and nickel (LaNiOx: LNO). The first electrode 10 may have asingle layer structure of any of the above exemplified materials or mayhave a structure in which several types of such materials are stacked.

For example, the first electrode 10 can be formed through vapordeposition, sputtering, or chemical vapor deposition (CVD). Then, aphotolithographic technique or the like can be employed to form apattern in the above shape. The first electrode 10 can be formed by atechnique such as a printing or imprinting technique. In this case, thefirst electrode 10 can be directly formed on the substrate 1.

1.1.3. Piezoelectric Layer

The piezoelectric layer 20 is formed so as to cover the first electrode10. In the case where the first electrode 10 is patterned, thepiezoelectric layer 20 may be formed on the substrate 1. Thepiezoelectric layer 20 has a region that is positioned between the firstelectrode 10 and the second electrode 30. Such a region of thepiezoelectric layer 20 is herein referred to as an active region 20 a,where appropriate. In a plan view, the active region 20 a of thepiezoelectric layer 20 corresponds to the overlap region 50 in which thefirst electrode 10 overlaps the second electrode 30.

Although the piezoelectric layer 20 is formed so as to cover the firstelectrode 10 and has the active region 20 a, a region (inactive region)other than the overlap region 50 (active region 20 a) may have a portionin which the piezoelectric layer 20 is not formed. For example, withreference to FIG. 1, through-holes 22 are formed in the inactive regionsof the piezoelectric layer 20. For example, the formation of thethrough-holes 22 in the piezoelectric layer 20 can contribute tosuppressing the defective vibration of the substrate 1 caused by thepiezoelectric layer 20.

In this embodiment, the piezoelectric layer 20 is formed so as to coverthe first electrode 10, and the piezoelectric layer 20 can thereforeprotect the first electrode 10 from, for example, impurities thatintrude from the outside.

Another layer may be formed between the first electrode 10 and thepiezoelectric layer 20. Examples of such another layer include atitanium layer. In the example in FIG. 1, the piezoelectric layer 20 isformed so as to contact the first electrode 10. For example, thepiezoelectric layer 20 can be configured so as to have a thickness thatis in the range from 100 to 2000 nm. In the case where the thickness ofthe piezoelectric layer 20 falls within such a range, the sufficientdeformation (electromechanical transduction) of the piezoelectric device100 (piezoelectric actuator 102) can be secured. More preferably, thepiezoelectric layer 20 has a thickness that is in the range from 1000 to1500 nm. In the case where the thickness of the piezoelectric layer 20falls within such a range, the piezoelectric device 100 can be deformedin a sufficiently large amount, and such a thickness can contribute tothinning the piezoelectric device 100.

The piezoelectric layer 20 is formed so as to primarily contain an oxidehaving a perovskite crystal structure and has piezoelectric properties.Examples of such an oxide having a perovskite crystal structure and usedfor the piezoelectric layer 20 include an oxide having a chemicalcomposition represented by a general formula M_(A)M_(B)O₃ (in thegeneral formula, an atom of an element corresponding to a site M_(A) iscoordinated to 12 oxygen atoms, and an atom of an element correspondingto a site M_(B) is coordinated to six oxygen atoms). The oxide that isemployed as the primary component of the piezoelectric layer 20 is notspecifically limited as long as piezoelectric properties are exhibited.On the basis of the general formula M_(A)M_(B)O₃, preferable examples ofsuch an oxide include an oxide which contains at least one elementselected from the group consisting of lead, potassium, barium,strontium, and bismuth as the element corresponding to the site M_(A)and which contains at least one element selected from the groupconsisting of zirconium, titanium, niobium, sodium, tantalum, andlanthanum as the element corresponding to the site M_(B).

Among these, an oxide at least containing lead, zirconium, titanium, andoxygen is more preferably employed as the primary component of thematerial used for the piezoelectric layer 20. Specific examples of theoxide preferably employed as the primary component of the piezoelectriclayer 20 include lead zirconate titanate [Pb(Zr,Ti)O₃] (hereinafterreferred to as PZT in short, where appropriate) and lead zirconatetitanate niobate [Pb(Zr,Ti,Nb)O₃] (hereinafter referred to as PZTN inshort, where appropriate).

such oxides can form a solid solution containing an oxide of the elementcorresponding to the site M_(A) and containing an oxide of the elementcorresponding to the site M_(B). Such a composite oxide can becrystallized, thereby being able to have the perovskite crystalstructure. Such an oxide has the perovskite crystal structure, therebybeing able to exhibit the piezoelectric properties. Accordingly, thepiezoelectric layer 20 can be deformed as a result of applying anelectric field through the first electrode 10 and the second electrode30 (namely, electromechanical transduction). The deformation of thepiezoelectric layer 20 enables the piezoelectric device 100 to bedeformed. Accordingly, for example, in the case where the substrate 1serves as a vibrating plate, the substrate 1 can be deformed (bent) andcan be vibrated.

The piezoelectric layer 20 may have a stack structure. For example,several layers including piezoelectric layers having differentcompositions or including piezoelectric layers having the samecompositions may be stacked. Furthermore, the piezoelectric layer 20 mayhave a composition gradient in a thickness direction. Moreover, thenumber of the layers to be stacked is appropriately determined.

For example, the piezoelectric layer 20 can be formed by a thin filmmethod such as: a sputtering method [including a direct current (DC)sputtering, ion sputtering, and magnetron sputtering method]; a vapordeposition method; a metalorganic chemical vapor deposition (MOCVD)method; a metal-organic decomposition (MOD) method; a pulsed laserdeposition (PLD) method (for example, a laser ablation method); a misteddeposition method; or a sol-gel method. For example, in the case wherethe piezoelectric layer 20 having a large thickness is formed by such athin film method, the piezoelectric layer 20 can be formed as a resultof securing long deposition time in an approach in which a material isdeposited, such as the sputtering method, vapor deposition method, orMOCVD method. Alternatively, in the case where an approach in whichcoating and calcination are performed is employed, such as the MODmethod or sol-gel method, such an approach is repeated to stack layers,thereby being able to form the piezoelectric layer 20. In the case wherethe layers are further stacked, different thin film methods may beemployed for individual layers, thereby stacking the layers.

1.1.4. Second Electrode

The second electrode 30 is formed on the piezoelectric layer 20. Thesecond electrode 30 is provided on the piezoelectric layer 20 but is notrequired to entirely cover the piezoelectric layer 20. In the case wherethe through-holes 22 or the likes are formed in the piezoelectric layer20, the second electrode 30 may be formed, for example, on the substrate1 at a portion at which the through-holes 22 or the likes are formed.The second electrode 30 is provided so as to have an area that forms astructure in which the piezoelectric layer 20 is positioned between suchan area and the first electrode 10 that is covered with thepiezoelectric layer 20. The second electrode 30 is provided in the formof a layer, a thin film, or a flat plate. For example, the secondelectrode 30 can be configured so as to have a thickness that is in therange from 20 nm to 300 nm. In the case where the second electrode 30has a thickness smaller than 20 nm, the electrical conductivity of thesecond electrode 30 may fall into insufficiency.

Seeing the second electrode 30 in a plan view (in a direction normal tothe substrate 1), the second electrode 30 forms an overlap region 50 inwhich the second electrode 30 overlaps the first electrode 10. Theoverlap region 50 has a rectangular shape in a plan view. A short side50 b of the overlap region 50 is defined by the second electrode 30. Forexample, the second electrode 30 has a rectangular shape in a plan view.In the case where the piezoelectric device 100 has a plurality ofoperable portions, the second electrode 30 can serve as a commonelectrode thereof.

In one of the functions of the second electrode 30, the second electrode30 serves as either electrode provided to apply an electric field to thepiezoelectric layer 20 (for example, an upper electrode that is formedso as to overlie the piezoelectric layer 20).

The same material as used for the first electrode 10 can be used for thesecond electrode 30. The second electrode 30 may have a single layerstructure of any of the above exemplified materials or may have astructure in which several types of materials are stacked. Among thematerials, iridium is employed as a primary component to form the secondelectrode 30, so that the electrical conductivity of the secondelectrode 30 becomes excellent, and an advantageous effect can beenhanced, in which the second electrode 30 protects the piezoelectriclayer 20 from moisture or hydrogen that intrudes from the outside, forexample.

For example, the second electrode 30 can be formed through vapordeposition, sputtering, or CVD. Then, a photolithographic technique orthe like can be employed to form a pattern in the above shape. Thesecond electrode 30 can be formed by a technique such as a printing orimprinting technique.

1.1.5. Overlap Region

As described above, the first electrode 10 and the second electrode 30form the overlap region 50 in which the first electrode 10 overlaps thesecond electrode 30 in a plan view. The overlap region 50 has arectangular shape in a plan view. In a plan view, the long side 50 a ofthe rectangular overlap region 50 is defined by the first electrode 10,and the short side 50 b is defined by the second electrode 30.

The overlap region 50 has a pair of first regions 51 that are providedadjacent to a pair of the short sides 50 b. The first regions 51 arepositioned at the two ends of the rectangular overlap region 50 in alength direction in a plan view. Namely, the first regions 51 aredefined as regions other than the central portion of the rectangularoverlap region 50 in a length direction in a plan view. In a plan view,each of the first regions 51 has an area that is larger than or equal to2% and that is less than 98%, relative to the area of the overlap region50. In view of more preferable balance between suppression of thedeformation, which is generated at the boundary between the activeregion 20 a and inactive region of the piezoelectric layer 20, andmagnitude of the deformation of the active region 20 a of thepiezoelectric layer 20, each of the first regions 51 more preferably hasan area that is larger than or equal to 10% and that is less than 80%,relative to the area of the overlap region 50 in a plan view.

The overlap region 50 has a second region 52 that is positioned betweenthe pair of the first regions 51. The second region 52 includes thecentral portion of the rectangular overlap region 50 in a lengthdirection in a plan view. Namely, the second region 52 is defined as aregion other than the two ends of the rectangular overlap region 50 in alength direction in a plan view. In a plan view, the second region 52has an area that is larger than or equal to 2% and that is less than98%, relative to the area of the overlap region 50. In view of morepreferable balance between suppression of the deformation, which isgenerated at the boundary between the active region 20 a and inactiveregion of the piezoelectric layer 20, and magnitude of the deformationof the active region 20 a of the piezoelectric layer 20, the secondregion 52 more preferably has an area that is larger than or equal to20% and that is less than 90%, relative to the area of the overlapregion 50 in a plan view.

1.1.6. Coating Layer

The coating layer 40 is formed on the second electrode 30. The coatinglayer 40 is provided so as to avoid the second region 52 of the overlapregion 50 in a plan view. Furthermore, the coating layer 40 is formed atleast in each of the first regions 51 of the overlap region 50 in a planview. The coating layer 40 may be provided at another portion on thesecond electrode 30. The coating layer 40 is not required to be providedentirely in the other region on the second electrode 30 than the secondregion 52. The coating layer 40 can be configured so as to have athickness that is, for example, in the range from 20 to 200 nm. Thecoating layer 40 is formed by using tungsten or titanium.

In one of the functions of the coating layer 40, in the case where anelectric field is applied to the drive region (overlap region 50) of thepiezoelectric layer 20 to generate the deformation, the coating layer 40suppresses the deformation of the piezoelectric layer 20 positioned inthe first regions 51. In another function of the coating layer 40, thecoating layer 40 serves as an aid for the electrical conductivity of thesecond electrode 30.

The coating layer 40 is provided at the outer side from the long side 50a positioned in the second region 52 of the overlap region 50 in a planview. Therefore, the coating layer 40 suppresses the deformation of theactive region 20 a of the piezoelectric layer 20 in a direction of theshort side 50 b in a small amount. Accordingly, the piezoelectric layer20 can deform in a sufficiently large amount.

1.1.7. Other Configurations

The piezoelectric device 100 of this embodiment may have a leadelectrode 60, the lead electrode 60 being formed on the piezoelectriclayer 20 and being electrically connected to the first electrode 10.

The planar shape of the lead electrode 60 is not specifically limited aslong as the lead electrode 60 is electrically connected to the firstelectrode 10 and is electrically isolated from the second electrode 30.

For example, the lead electrode 60 is formed as follows: a through-hole20 b is formed in the piezoelectric layer 20 so as to be incommunication with the first electrode 10; a base layer 62 is formedinside the through-hole 20 b and in a desired region on thepiezoelectric layer 20 by using an alloy of nickel and chromium; and alead electrode layer 64 is then formed on the base layer 62 as a resultof, for example, stacking gold.

Although a material used for the lead electrode 60 is not specificallylimited, the alloy of nickel and chromium is used to at least form thebase layer 62 with the result that adhesion between the piezoelectriclayer 20 and the lead electrode 60 can be increased.

In one of the functions of the lead electrode 60, electrical connectionto the first electrode 10 can be formed on the piezoelectric layer 20while a state in which the piezoelectric layer 20 covers the firstelectrode 10 is maintained. Accordingly, for example, an electricalconnection between the first electrode 10 and an outside portion can beeasily formed during a production process. By virtue of such aconfiguration, for example, the occupied area of the piezoelectricdevice 100 can be decreased in a plan view, thereby being able toimprove the density of arrangement of nozzle holes 612 of theliquid-ejecting head 1000.

1.1.8. Characteristics of Piezoelectric Device

The piezoelectric device 100 (piezoelectric actuator 102) of thisembodiment has the following characteristics.

In the piezoelectric device 100 of this embodiment, the coating layer 40is made of tungsten or titanium. Tungsten or titanium is a material thatexhibits a relatively high Young's modulus. The coating layer 40 made ofsuch a material is formed on the first regions 51, so that thedeformation of the piezoelectric layer 20 in the first regions 51 can besuppressed to a smaller level relative to the natural deformationamount. On the other hand, the coating layer 40 is not formed in thesecond region 52, and the deformation of the piezoelectric layer 20 inthe second region 52 is not therefore suppressed, so that thedeformation of the piezoelectric device 100 can be secured in asufficiently large amount.

Meanwhile, stress generated in the piezoelectric layer 20 will bedescribed. An electric field is applied through the first electrode 10and the second electrode 30 with the result that the active region 20 aof the piezoelectric layer 20 deforms, for example, in the manner ofexpansion and contraction. In this case, an electric field is not almostapplied to regions, which are adjacent to the active region 20 a, of thepiezoelectric layer 20, and the deformation is not caused. Therefore,the deformation is restricted at a boundary with such regions, andstress is generated. The stress is generated when the active region 20 aexpands and contracts in a plane of the piezoelectric layer 20, andstress having a piezoelectric layer 20-pulling component is generatedespecially in the case where active region 20 a contracts. In the casewhere the stress is increased to a certain magnitude or larger, crackingoccurs at a boundary between the active region 20 a and inactive regionof the piezoelectric layer 20. Because the active region 20 a (overlapregion 50) has a long side, such cracking is likely to occur at an endof the active region 20 a in a length direction (position parallel tothe short side 50 b of the overlap region 50) before cracking occurs atother portions, such an end having an increased expansion component.

Meanwhile, the stress that causes cracking in the piezoelectric layer 20depends on an amount in which the deformation is restricted.Specifically, in the case where the deformation is restricted in largeamounts, the stress is generated in larger amounts. Accordingly, thelarger difference in the deformation amount between adjacent regions inthe piezoelectric layer 20 becomes, the larger stress is generated. Incontrast, the difference in the deformation amount between adjacentregions in the piezoelectric layer 20 is decreased, thereby being ableto decrease the amount of the stress to be generated.

In the piezoelectric device 100 of this embodiment, the coating layer 40is formed in the first regions 51 that are positioned so as tocorrespond to ends of the active region 20 a in a length direction.Therefore, the coating layer 40 can serve to suppress the deformation ofthe ends of the active region 20 a in a length direction to a smallerlevel relative to the natural deformation amount. Accordingly, an amountin which the deformation generated at the boundary between the activeregion 20 a and the inactive region is restricted can be decreased, andthe stress generated at such a boundary can be decreased. Consequently,the piezoelectric device 100 of this embodiment has an advantage inwhich the formation of the coating layer 40 enables the stress generatedin the piezoelectric layer 20 to be suppressed and in which breakingsuch as cracking is therefore less likely to be caused in thepiezoelectric layer 20.

Each of tungsten and titanium used as a material of the coating layer 40has standard electrode potential close to that of each of nickel andchromium. Specifically, standard electrode potential in each ofreactions of WO₂+4H⁺+4e⁻←→W+2H₂O and W₂O₅+2H⁺+2e⁻←→W+2H₂O is −0.119 V,standard electrode potential in a reaction of Ti²⁺+2e⁻←→Ti is −1.63 V,and standard electrode potential in a reaction of Ti³⁺+e⁻←→Ti²⁺ is−0.360 V. On the other hand, standard electrode potential in a reactionof Ni²⁺+2e⁻←→Ni is −0.257 V, and standard electrode potential in areaction of Cr²⁺+2e⁻←→Cr is −0.9 V.

Meanwhile, standard electrode potential in a reaction of Ir³⁺+3e⁻←→Ir is+1.156 V.

In the case of a configuration in which the lead electrode 60 containingnickel and chromium is provided and in the case where wet etching isrequired to be performed for process reasons, the coating layer 40 isprovided on the second electrode 30, thereby being able to suppressgalvanic corrosion of nickel or chromium to a reduced amount, suchgalvanic corrosion being caused by etchant. Namely, in the case wherethe coating layer 40 is not formed, iridium that exhibits high standardelectrode potential and each of nickel and chromium that exhibits lowstandard electrode potential are immersed into the etchant in such anetching process, and an electrochemical reaction is likely to be caused.In contrast, the piezoelectric device 100 of this embodiment has thefollowing advantage: in a configuration in which the lead electrode 60containing nickel and chromium is provided, the formation of the coatinglayer 40 can contribute to decreasing an area in which iridium contactsthe etchant. Furthermore, in such an advantage, iridium is covered withtungsten or titanium having standard electrode potential close to thatof each of nickel and chromium, such an electrochemical reaction istherefore suppressed, and galvanic corrosion of nickel and chromium isaccordingly less likely to be caused.

1.2. Other Configurations

The liquid-ejecting head 1000 of this embodiment has the piezoelectricdevice 100, a vibrating plate 1 a, a pressure chamber substrate 620, anda nozzle plate 610. Use of vibrating plate 1 a for the liquid-ejectinghead 1000 corresponds to the case in which the substrate 1 serves as avibrating plate as described with respect to the piezoelectric device100. In FIG. 1, illustration of the nozzle plate 610 is omitted.

The nozzle plate 610 has a nozzle hole 612. The nozzle hole 612 iscapable of ejecting ink. For example, a plurality of the nozzle holes612 are formed in the nozzle plate 610 in line (see, FIG. 4). Examplesof a material used for the nozzle plate 610 include silicon and steelused stainless (SUS).

The pressure chamber substrate 620 is disposed so as to overlie thenozzle plate 610 (underlying the nozzle plate 610, in FIG. 4). Examplesof a material used for the pressure chamber substrate 620 includesilicon. The pressure chamber substrate 620 defines a space between thenozzle plate 610 and the vibrating plate 1 a, and the liquid-ejectinghead 1000 is therefore provided with a reservoir (liquid-reservingsection) 624, a feed opening 626 connected to the reservoir 624, and thepressure chamber 622 connected to the feed opening 626 as illustrated inFIG. 4. The reservoir 624, the feed opening 626, and the pressurechamber 622 are flow channels of the liquid. Although the flow channelsare individually described in this embodiment, they may be designed inany manner. In addition, for example, although part of the flow channelsis narrowed to form the feed opening 626 in the illustration, such aconfiguration is not indispensable, and the feed opening 626 may beformed on the basis of an appropriate design. The reservoir 624, thefeed opening 626, and the pressure chamber 622 are defined by the nozzleplate 610, the pressure chamber substrate 620, and the vibrating plate 1a. The reservoir 624 is capable of temporarily reserving an ink that issupplied from the outside (an ink cartridge, for example) through athorough-hole 628 formed in the vibrating plate 1 a. The ink inside thereservoir 624 can be supplied to the pressure chamber 622 through thefeed opening 626. The vibrating plate 1 a is deformed, and the volume ofthe pressure chamber 622 is therefore changed. The pressure chamber 622is connected to the nozzle hole 612. The volume change in the pressurechamber 622 enables ink or the like to be ejected from the nozzle hole612.

The piezoelectric device 100 is disposed so as to overlie the pressurechamber substrate 620 (underlying the pressure chamber substrate 620, inFIG. 4). The piezoelectric device 100 can be electrically connected to apiezoelectric device-driving circuit (not illustrated) and can beactuated on the basis of a signal transmitted from the piezoelectricdevice-driving circuit. The vibrating plate 1 a is deformed depending onthe action of the piezoelectric device 100 and is therefore capable ofappropriately changing the inner pressure of the pressure chamber 622.

With reference to FIG. 4, a housing 630 is capable of accommodating thenozzle plate 610, the pressure chamber substrate 620, and thepiezoelectric device 100. Examples of a material used for the housing630 include resin and metal.

The liquid-ejecting head 1000 has the piezoelectric device 100.Accordingly, breaking such as cracking is not less likely to be causedin the piezoelectric layer 20, and high reliability is thereforeprovided.

For example, the liquid-ejecting head 1000 of this embodiment can bepreferably utilized for the following applications: a recording headused for an image-recording apparatus such as a printer; a colormaterial-ejecting head used for manufacturing a color filter of a liquidcrystal display or the like; a liquid material-ejecting head used forforming an electrode or color filter of an organic electro-luminescence(EL) display, field emission display (FED), electrophoretic display, orthe like; and a living-organic material-ejecting head used formanufacturing a biochip.

In the above description, an example of the piezoelectric device(piezoelectric actuator) of embodiments of the invention has beenprovided, in which the substrate 1 is provided in the form of thevibrating plate 1 a that is deformed in the manner of, for example,bending. Examples of the piezoelectric device (piezoelectric actuator)of embodiments of the invention include other types of piezoelectricdevices including: a timing device in which the substrate 1 is providedin the form of a vibration piece having a tuning fork-like shape; anultrasonic device such as an ultrasonic oscillator in which thesubstrate 1 is vibrated in a frequency of an ultrasonic range togenerate ultrasonic wave; a device having a mechanical output, such asan ultrasonic motor in which the substrate 1 is vibrated in a frequencyof an ultrasonic range to drive another component; and a pressure sensorwhich detects the stress applied to the substrate 1 and the deformationof the substrate 1.

2. Liquid-Ejecting Apparatus

FIG. 5 is a perspective view schematically illustrating aliquid-ejecting apparatus 2000.

With reference to FIG. 5, the liquid-ejecting apparatus 2000 includes ahead unit 730, a driving section 710, and a control section 760.Furthermore, the liquid-ejecting apparatus 2000 is capable of includingan apparatus body 720, a paper feed section 750, a paper feed tray 721on which recording paper P is placed, an ejection opening 722 throughwhich the recording paper P is ejected, and an operation panel 770disposed at an upper surface of the apparatus body 720.

The head unit 730 has the liquid-ejecting head 1000 (hereinafterreferred to as “head”, simply). Furthermore, the head unit 730 has anink cartridge 731 which supplies ink to the head and has a transportingunit (carriage) 732 on which the head and the ink cartridge 731 aremounted.

The driving section 710 enables the head unit 730 to be reciprocated.The driving section 710 has a carriage motor 741 that serves as adriving source of the head unit 730 and has a reciprocating mechanism742 that reciprocates the head unit 730 by receiving the rotation of thecarriage motor 741.

The reciprocating mechanism 742 includes a carriage guide shaft 744 ofwhich two ends are supported by a frame (not illustrated) and includes atiming belt 743 extending in parallel with the carriage guide shaft 744.The carriage 732 is supported by the carriage guide shaft 744 so as tobe able to be reciprocated. Furthermore, the carriage 732 is fixed topart of the timing belt 743. The carriage motor 741 is operated to workthe timing belt 743, and the head unit 730 is therefore reciprocatedwhile being guided by the carriage guide shaft 744. During thereciprocation, ink is appropriately ejected from the head to performprinting to the recording paper P.

In this embodiment, although printing is performed while theliquid-ejecting head 1000 and the recording paper P are moved, theliquid-ejecting apparatus of embodiments of the invention may have aconfiguration in which printing is performed to the recording paper Pwhile the liquid-ejecting head 1000 and the recording paper P relativelychange positions each other. Furthermore, although printing is performedto the recording paper P in this embodiment, a recording medium to whichprinting can be performed by the liquid-ejecting apparatus ofembodiments of the invention is not limited to paper. Examples of such amedium variously include cloth, a film, and metal, and the configurationof the apparatus may be appropriately changed.

The control section 760 is capable of controlling the head unit 730, thedriving section 710, and the paper feed section 750.

The paper feed section 750 is capable of transporting the recordingpaper P from the paper feed tray 721 toward the head unit 730. The paperfeed section 750 includes a paper feed motor 751 that serves as adriving source thereof and includes a paper feed roller 752 that rotatesby the operation of the paper feed motor 751. The paper feed roller 752includes a driven roller 752 a and a driving roller 752 b, and thedriving roller 752 b is disposed above the driven roller 752 a so as toface each other while a transport path of the recording paper P isinterposed therebetween. The driving roller 752 b is connected to thepaper feed motor 751. The control section 760 drives the paper feedsection 750, and then the recording paper P is transported so as to passbelow the head unit 730.

The head unit 730, the driving section 710, the control section 760, andthe paper feed section 750 are provided inside the apparatus body 720.

The liquid-ejecting apparatus 2000 has the liquid-ejecting head 1000.Therefore, excellent reliability is provided.

The above exemplified liquid-ejecting apparatus 2000 has a singleliquid-ejecting head 1000, and the liquid-ejecting head 1000 canfunction to perform printing to a recording medium. However, a pluralityof the liquid-ejecting heads may be provided. In the case where theliquid-ejecting apparatus includes the plurality of the liquid-ejectingheads, the liquid-ejecting heads may be individually operated in theabove manner, or the liquid-ejecting heads may be connected to eachother to form an integrated head. An example of such an integrated headincludes a line-type head in which individual nozzle holes of the headsare overall positioned so as to be spaced at a uniform distance.

Although the liquid-ejecting apparatus 2000 that serves as an ink jetprinter has been described as an example of the liquid-ejectingapparatus having the liquid-ejecting head with the piezoelectric device(piezoelectric actuator) of embodiments of the invention, theliquid-ejecting apparatus of embodiments of the invention may be alsoapplied to industrial use. In this case, various functional materialsthat are prepared with a solvent or a dispersion medium so as to haveappropriate viscosity may be used as liquid or the like (liquidmaterial) to be ejected. The liquid-ejecting apparatus of embodiments ofthe invention can be preferably applied not only to the exemplifiedimage-recording apparatus, such as a printer, but also to a colormaterial-ejecting apparatus used for manufacturing a color filter of aliquid crystal display or the like; a liquid material-ejecting apparatusused for forming an electrode and color filter of an organic EL display,FED, electrophoretic display, or the like; and a living-organicmaterial-ejecting apparatus used for manufacturing a biochip.

3. Experimental Example

An experimental example will be hereinafter described for the purpose ofmore detailed description of embodiments of the invention. Embodimentsof the invention are not limited to the following experimental exampleat all.

3.1. Computer Experiment

An infinite element method was employed to evaluate shear strain thatwas generated at the boundary between the active region 20 a andinactive region of the piezoelectric layer 20 as described in the aboveembodiments.

In a model to be evaluated by the infinite element method, the firstelectrode 10 was formed by using platinum so as to have a thickness of200 nm, a PZT layer (piezoelectric layer) was then formed on the firstelectrode 10 so as to have a thickness of 1000 nm, and the secondelectrode 30 was then formed on the PZT layer by using iridium so as tohave a thickness of 50 nm. The overlap region 50 is configured so as tohave the long side 50 a with a length of 500 μm and so as to have theshort side 50 b with a length of 100 μm. The planar shape of the coatinglayer 40 was designed so as to cover the inner side of the overlapregion 50 in an area of 50 μm from the short side 50 b. In thisexperimental example, tungsten was employed as a material used for thecoating layer 40.

In the infinite element method, a Young's modulus was designed in eachof the materials as follows: 300 Gpa in iridium, 210 Gpa in tungsten,and 75 Gpa in PZT. A Poisson's ratio in each of iridium and tungsten wasdesigned to be 0.3.

The thickness of the coating layer 40 was varied from 0 to 150 nm, andshear strain generated when the piezoelectric layer 20 was actuated wascalculated. Meanwhile, provided that PZT was strained in the manner ofcontraction in an in-plane direction, shear strain generated when thepiezoelectric layer 20 was contracted by 0.00376% was obtained in eachcalculation.

The results were illustrated in FIG. 6. In FIG. 6, the lateral axisindicates the thickness of the coating layer 40, and the longitudinalaxis indicates the relative amount of the shear strain, such a relativeamount being normalized assuming that the shear strain of the coatinglayer 40 with a thickness of 0 nm was 1 (100%).

With reference to FIG. 6, it was found that the thickness of the coatinglayer 40 was increased accompanying the decrease of shear straingenerated at the boundary between the active region 20 a and inactiveregion of the piezoelectric layer 20. From this result, it was provedthat the formation of a coating layer 40 on a second electrode 30 couldcontribute to suppressing the stress generated at the boundary betweenthe active region 20 a and inactive region of the piezoelectric layer20.

3.2. Electron Microscope Observation

FIGS. 7 and 8 illustrate specimens which were micrographed using atransmission electron microscope and in which a tungsten layer and atitanium layer were respectively formed as the coating layer 40 on thesecond electrode 30 (iridium) provided on the piezoelectric layer 20(PZT).

With reference to FIGS. 7 and 8, in each of the specimens, the coatinglayer 40 was uniformly formed on the second electrode 30 without theoccurrence of a defect such as generation of a gap. Such a resultindicated that each of the piezoelectric layer 20, second electrode 30,and coating layer 40 had excellent adhesion. Accordingly, it wasconsidered that an advantage was provided, in which the coating layer 40could contribute to suppressing the strain generated in thepiezoelectric layer 20.

The above embodiments or the likes can be appropriately combined witharbitrary embodiments. Accordingly, the combined embodiments can exhibitthe effects of individual embodiments or can generate a synergisticeffect.

Embodiments of the invention are not limited to the above embodiment andcan be variously modified. For example, embodiments of the inventioninclude configurations substantially the same as those described in theabove embodiments (for example, configurations having the samefunctions, processes, and results or having the same objects andadvantageous effects as those in the above embodiments). In addition,embodiments of the invention may include configurations provided bychanging non-essential parts of the configurations described in theabove embodiments. Furthermore, embodiments of the invention may includeconfigurations that can provide effects the same as those described inthe above embodiments or that can provide advantages the same as thosedescribed in the above embodiments. Still furthermore, embodiments ofthe invention may include configurations in which at least onewell-known technique is added to the configurations described in theabove embodiments.

What is claimed is:
 1. A piezoelectric device comprising: a firstelectrode; a piezoelectric layer that is formed above the firstelectrode; a second electrode that is formed above the piezoelectriclayer; a coating layer that is formed above the second electrodeconsisting of tungsten, and a lead electrode that is formed on thepiezoelectric layer so as to be electrically connected to the firstelectrode, the lead electrode containing nickel and chromium.
 2. Thepiezoelectric device according to claim 1, wherein a material used forthe second electrode primarily contains iridium.
 3. A liquid-ejectingapparatus having the piezoelectric device according to claim
 1. 4. Aliquid-ejecting apparatus having the piezoelectric device according toclaim
 2. 5. The piezoelectric device according to claim 1, wherein thefirst electrode and the second electrode form a rectangular overlapregion in which the first electrode overlaps the second electrode in aplan view, the first electrode defining a long side of the overlapregion and the second electrode defining a short side of the overlapregion, the overlap region having a pair of first regions and having asecond region, the pair of the first regions being positioned adjacentto a pair of the short sides, and the second region being positionedbetween the pair of the first regions.
 6. The piezoelectric deviceaccording to claim 5, wherein the coating layer is formed at least inthe first regions so as to avoid the second region of the overlapregion.
 7. A piezoelectric device comprising: a first electrode; apiezoelectric layer that is formed above the first electrode; a secondelectrode that is formed above the piezoelectric layer; and a coatinglayer that is formed above the second electrode, wherein the firstelectrode and the second electrode form a rectangular overlap region inwhich the first electrode overlaps the second electrode in a plan view,the first electrode defining a long side of the overlap region and thesecond electrode defining a short side of the overlap region, theoverlap region having a pair of first regions and having a secondregion, the pair of the first regions being positioned adjacent to apair of the short sides, and the second region being positioned betweenthe pair of the first regions.
 8. The piezoelectric device according toclaim 7, wherein the coating layer is formed at least in the firstregions so as to avoid the second region of the overlap region.
 9. Thepiezoelectric device according to claim 7, wherein the coating layer isformed at a boundary between an active region and an inactive region ofthe piezoelectric layer, the active region being a region where thepiezoelectric layer is disposed between the first and second electrodesand the inactive region being a region where the piezoelectric layer isnot disposed between the first and second electrodes.
 10. Aliquid-ejecting apparatus having the piezoelectric device according toclaim
 7. 11. A liquid-ejecting apparatus having the piezoelectric deviceaccording to claim
 8. 12. A liquid-ejecting apparatus having thepiezoelectric device according to claim 9.